The present invention concerns a method for internal fixation of vertebra of the spine.
It has long been known that internal fixation is a adjunct to fusion, such as a transverse process fusion. In early prior art techniques, a surgeon made an incision in the patient's back and separated tissue and muscle in order to expose a wide area of the spine in which the procedure was to take place. The fusion and fixation in one prior art process is by grafting bone segments between opposing traverse processes of adjacent vertebrae. However, this technique resulted in gross destruction of normal anatomy as well as high blood loss. Moreover, this surgical technique did not completely stabilize the vertebra since there was no direct connection between the vertebral bodies.
In more recent times, a surgical technique known as dowel interbody fusion has been developed. In this technique, bores are formed in disc tissue through either open surgery or percutaneous surgery. A dowel is made to fit to the bores foed in the disc tissue. In still a further technique, all disc tissue is removed between adjacent vertebrae, as well as the disc plates. Large surface area bone grafts are then placed within the clean space to form a graft between the opposing vertebral bodies. In each of these latter two prior art processes it still remains necessary to provide some means for fixation to facilitate fusion of the large area bone graft or the dowel to the vertebrae.
Many types of instrumentation for performing spinal fixation are known in the art. For instance, spine instrumentation developed by Dr. Paul S. Harrington incorporates a hook and rod configuration, as described in his February 1973 publication by Zimmer, Inc., entitled "Harrington Spine Instrumentation and Fusion Technique. Implantation of the Harrington spinal instrumentation requires subperiosteal stripping of the spine to avoid injury to the muscular nerves and vessels. Dissection of the muscle tissue is also required. In some aspects of the early Harrington techniques, the spine was stripped clean of the supraspinous and intraspinous ligaments.
Later developed techniques involve hardware which is placed through the skin and through the muscle into the bone. Some of the fixation hardware remains outside the body, but is removed after the fusion has been completed. Techniques of this sort are characterized by high risk of pin tract infection and incisional morbidity.
Thus far, each of the prior art spinal fixation and/or fusion techniques have been characterized by excessive invasion into the patients spine and back region. What is needed is a technique which allows for adequate stabilization of the spine, yet decreases the chance of infection as well as patient morbidity. There is further a need for such a method which permits percutaneous removal of the fixation hardware as an outpatient procedure after fusion has been completed.